The present invention relates to a wafer processing method, and more particularly, to a wafer processing method which can improve the gettering characteristics of a wafer and reduce the total processing cost of the wafer.
When processing a silicon wafer, if the wafer is contaminated with metal impurities, in particular, transition metal impurities, through exposure brought about by various processes, and then the manufacturing yield and the reliability of a semiconductor device can decrease. This is because the metal impurities infiltrate and diffuse throughout the silicon wafer can subsequently compromise the performance of the resultant components in the silicon wafer. Metal impurities can infiltrate in to oxide layers and compromise the integrity of the insulative character of oxide layers. Metal impurities can also infiltrate and cause crystal defects. Metal impurities can also serve as deep level impurities. The insulation breakdown field strength of a gate oxide layer decreases as the amount of metal contamination increases. As the crystalline density of the oxide layer increases the allowable impurity concentration decreases due to thin-filming of the oxide layer.
Under these situations, various methods for minimizing contamination of a wafer by metal impurities have been proposed in the art. Recently, gettering technology for adsorbing metal impurities in the wafer itself is widely used.
The gettering is a technique of sequestering metal impurities away from active areas. Oftentimes gettering involves moving the metal impurities from the active region of the wafer to the bulk or the back side of the wafer. The procedure of the gettering technology generally involves a first step of releasing metal impurities from their places, a second step of diffusing the metal impurities to the bulk or the back side of the wafer, and a third step of capturing or sequestering the metal impurities at a gettering site away from the active region.
One particular mechanism of the gettering technology can be divided into segregation-induced gettering phase in which an ion-implantation layer, having an increased impurity solubility, is formed by doping boron adjacent to crystal defects at a high concentration so that metal impurities can be gathered to the ion-implantation layer. This is then followed by a relaxation-induced gettering phase that exploits the rapid diffusion characteristics of transition metal impurities in the wafer.
It is thought that the relaxation-induced gettering that exploits the rapid diffusion characteristics of transition metal impurities in the wafer can be divided into an intrinsic gettering (IG) method and an extrinsic gettering (EG) method. The intrinsic gettering (IG) method adopts a DZ (denuded zone) or a natural scheme. The extrinsic gettering (EG) method adopts a PBS (poly back seal), sand blast, laser or a ring.
However, while not shown in a drawing and not explained in detail, in the conventional gettering methods using IG and EG, while conducting a process, unwanted particles are likely to be produced by high pressure injection and high temperature annealing, so the continuity of gettering effect is degraded.
Also, due to the different physical properties of the transition metal impurities such as Fe, Ni and Cu in the wafer, limitations exist in using only one gettering method. As a result it can become difficult or impossible to accomplish a satisfactory sequestering of all of these various impurities along the gettering sites scattered over the entire area of the wafer.
Further, even if gettering can be successfully obtained in the initial stage of a process for forming devices, high temperature annealing implemented for extended periods and various other subsequent wafer forming processes, may result in deteriorating the efficiency of the initial gettering sequestration. Moreover, as one more additional layer is deposited, the manufacturing cost necessarily increases.
In order to cope with these problems, a method of forming a gettering site on the back side of the wafer to improve the gettering characteristics has been proposed. Nevertheless, even in this case, because the gettering site wafer can costs about 1.8 times higher than a normal wafer, the cost of the entire wafer forming processes increases.
Therefore, a method capable of improving gettering characteristics while decreasing the cost of entire wafer forming processes is keenly demanded in the art.